1. Field of the Invention
The invention pertains generally to gimbal systems of the type used to support antenna units. More particularly, the invention relates to a bearing used to support the gimbal rings of such systems.
2. Description of the Prior Art
In many applications, it is important that a platform maintain a precise orientation irrespective of the movements of the platform's support. Traditionally, this has been accomplished by mounting the platform within a concentric arrangement of inner and outer gimbal rings. Typical gimbal systems of this sort include a mounting base, an outer gimbal ring rotatably attached to the mounting base, and an inner gimbal ring rotatably attached to the outer ring for rotation about an axis that is perpendicular to the rotational axis of the outer ring. This structure allows a platform attached to the inner ring to stabilize, or maintain its line of sight, even though the support of the platform is unsteady. The limits of this line of sight define a "look angle", determined by the shape of the outer gimbal ring. The shape of the outer ring is, among other things, dictated by the bearing used to attach it to the mounting base. This bearing must not only allow the inner gimbal ring and platform to be able to swing through a large look angle, but, in the case in which sensitive electronics are involved, must also provide an extremely steady, low vibration coupling to the outer ring base.
There are numerous prior art bearing designs for maintaining precision gimbal ring alignment and movement. They all, however, have certain deficiencies. Current methods of aligning the outer gimbal ring involve the use of bearing races which are a part of the outer edges of the gimbal ring itself. A common scheme is to allow the outer ring to ride upon several relatively large rollers. The effect of this design is a concentration of vibrational and other loadings over a small segment of the ring. Another prior art method is to fashion a recirculating bearing path in the platform base. The path is positioned to allow circulating balls to contact bearing races on the outer edges of the gimbal ring. Dimensional limitations require the balls to negotiate tight corners, lessening the smoothness of the gimbal ring movement.